Never mind Copenhagen. Never mind Congress: President Obama’s over- reachers intend unilaterally to lower the Earth’s temperature — or kill the US economy trying.

In a radical move that stands to destroy countless American jobs, the Environmental Protection Agency yesterday finalized a rule that designates carbon dioxide a threat that must be regulated.

The move paves the way for the agency to order an economically crippling cap on emissions by power plants, factories, even motor vehicles — the very same cap that Congress has so far refused to OK.

But the EPA’s brief doesn’t extend to India and China — or any other country. So think of the diktat as unilateral economic disarmament — a self-imposed tariff payable only in US jobs and future prosperity.

The timing of the announcement was no accident, of course.

The global summit on climate change opened yesterday in Copenhagen, and participants will cheer Washington’s action — even as they reject any binding caps on themselves.

But make no mistake: The consequences for Americans will be extreme.

“This action poses a threat to every American family and business,” says Jack Gerard, president of the American Petroleum Institute. “It could chill job growth and delay business expansion.”

“Individual American consumers and businesses alike will be dramatically affected by this decision,” Charles Drevna, president of the National Petrochemical & Refiners Association, insists. He says the move “is based on selective science, a weak legal and policy foundation and a failure to account for numerous uncertainties.”

Actually, the agency itself explicitly admits that last part: “The [EPA] administrator acknowledges the many uncertainties in these areas,” the finding says.

But that’s been clear since April, when the EPA proposed the finding; it terms its approach “precautionary policy.”

As The Wall Street Journal’s Daniel Henninger notes, under this approach, “precautionary measures” are OK if “an activity raises threats of harm to the environment or human health . . . even if some cause-and-effect relationships are not fully established scientifically.”

Not the least of the “uncertainties,” of course, is whether capping carbon emissions at any level will have the slightest impact on the environment.

If the so-called Climategate e-mail scandal demonstrates anything, it’s that nobody knows with even modest certainty whether carbon caps will have any impact on the environment at all.

But this means nothing to the EPA. It says it doesn’t need hard science to back its power grab.